1. Field of the Invention
The invention relates to a control apparatus and a control method for a negative pressure generating apparatus. More specifically, the invention relates to a control apparatus and a control method for a negative pressure generating apparatus, which make an ejector function according to a magnitude of a negative pressure to be taken from an intake passage.
2. Description of the Related Art
In a vehicle, an ejector is used to supply a negative pressure whose magnitude is larger than that of a negative pressure to be taken from an intake passage (for example, an intake manifold or a surge tank) in an intake system for an internal combustion engine, to a negative pressure operating device such as a brake booster (hereinafter, the negative pressure to be taken from the intake passage may be referred to as “intake pipe negative pressure”). The ejector is described, for example, in Japanese Patent Application Publication No. 2005-297654 (JP-A-2005-297654).
The magnitude of the intake pipe negative pressure is generally largest when the internal combustion engine is idling. Therefore, the magnitude of the negative pressure in the negative pressure operating device is generally sufficiently large when the internal combustion engine is idling. When the ejector does not function, the intake pipe negative pressure is supplied to the negative pressure operating device. However, even when the internal combustion engine is idling, the magnitude of the intake pipe negative pressure varies under various conditions. That is, even when the internal combustion engine is idling, the magnitude of the intake pipe negative pressure may be small, and may not be sufficiently large for the negative pressure operating device.
In this case, by making the ejector function, the negative pressure, whose magnitude is larger than that of the intake pipe negative pressure, can be supplied to the negative pressure operating device. Therefore, it is preferable to make the ejector function, for example, when the intake pipe negative pressure is a negative value larger than a predetermined value. Further, it is possible to make the ejector function also when the internal combustion engine is idling, by executing a control that makes the ejector function when an opening degree of a throttle valve is smaller than a predetermined opening degree (i.e., the predetermined opening degree that is close to, and larger than an opening degree when the internal combustion engine is idling), to ensure that the magnitude of the negative pressure in the negative pressure operating device is sufficiently large when the internal combustion engine is idling.
However, when the ejector functions in the above-described manner, the following problem occurs. FIG. 4 is a diagram showing the intake pipe negative pressure, operation of the ejector in related art, and the opening degree of the throttle valve when the vehicle travels. In FIG. 4, when the intake pipe negative pressure is a negative value larger than the predetermined value as described above, and the opening degree of the throttle valve is smaller than the predetermined opening degree, the ejector functions.
As shown in FIG. 4, when the throttle valve is opened, the magnitude of the negative pressure is decreased, that is, the negative value indicating the negative pressure is increased. Then, when the throttle valve is closed after the vehicle is steadily accelerated, the magnitude of the intake pipe negative pressure is increased, that is, the negative value indicating the negative pressure is decreased. At this time, the vehicle is decelerated. However, the change in the intake pipe negative pressure lags behind the change in the opening degree of the throttle valve. Therefore, a situation occurs in which the intake pipe negative pressure is a negative value larger than the predetermined value (i.e., a negative pressure determination value in FIG. 4) when the opening degree of the throttle valve is smaller than the predetermined opening degree.
That is, in this situation, the intake pipe negative pressure is a negative value larger than the predetermined value, and the opening degree of the throttle valve is smaller than the predetermined opening degree. Accordingly, the ejector functions in this situation. However, immediately after that, the intake pipe negative pressure becomes a negative value equal to or smaller than the predetermined value, and therefore, the ejector stops functioning. That is, in this case, the ejector is momentarily operated, and immediately after that, the intake pipe negative pressure becomes a negative value equal to or smaller than the predetermined value (i.e., the ejector functions and stop functions). Thus, the ejector may be unnecessarily operated when the vehicle is transiently decelerated, and the change in the intake pipe negative pressure lags behind the change in the opening degree of the throttle valve.